The present invention relates to a measuring system and a method for evaluating the condition of a patient.
The blood refill time is one of indexes for knowing the tissue perfusion of the subject. The blood refill time is handled as a simple index for evaluating whether shock occurs or not. The blood refill time is widely used in the field of emergency medicine in order to determine necessity/unnecessity of transfusion, triage category (evaluation of the priority in the case where many persons are injured or sickened), or the like. Also with respect to the degree of oxygenation of blood (arterial oxygen saturation), the blood refill time is important to determine whether blood is sufficiently supplied to the living tissue or not.
In usual measurement of the blood refill time, a medical person compresses the living tissue of the subject, such as a finger nail, and, after the compression is released, visually checks the color change of the nail or the skin. When the color returns to the original one within approximately two seconds, it is determined that the subject is in the normal condition. In the technique, however, the living tissue is manually compressed, and the change of the skin color is visually checked. Therefore, the technique has poor quantitative performance, and a measurement error easily occurs.
Therefore, a technique in which the blood refill time is measured by using a mechanism similar to a pulse oximeter has been proposed (JP-A-2012-115640). In the technique, light of a wavelength which can be absorbed by blood enters living tissue (mainly, the fingertip), and the intensity of light which transmits through the living tissue is measured by an optical sensor. In this case, when the living tissue is compressed by using an actuator, blood is evacuated from the living tissue of the compressed portion, and hence the intensity of the transmitted light is increased.
When the compression is released, the living tissue of the portion is filled with blood, and therefore the intensity of the transmitted light is decreased. The blood refill time is identified based on the time period which elapses after the release of the compression until the transmitted light intensity returns to the original level.
It is known that the blood flow in the vicinity of the fingertip is largely affected by the temperature and the activity of the nervous system. By contrast, the blood flow in the vicinity of the forehead is less affected by the temperature and the activity of the nervous system. Also with respect to a measurement of the percutaneous arterial oxygen saturation (SpO2) using a pulse oximeter, it is known that it cannot be measured in the fingertip because the peripheral circulation is poor, but, in the forehead, the measurement is highly possible.
Also in a measurement of the blood refill time, a waveform which is measured in the vicinity of the fingertip is affected by both the peripheral circulation and the central circulation. Even in the above-described technique in which the measurement is performed based on the detection of transmitted light, therefore, the value of the blood refill time which is measured in the vicinity of the fingertip is sometimes different from that which is measured in the vicinity of the forehead.
In the case where the subject suffers arteriosclerosis obliterans (ASO), moreover, the value of the blood refill time which is measured in the fingertip of one of the hands is sometimes different from that which is measured in the fingertip of the other hand. That is, the blood refill time that is measured in the hand in which the obstruction in a blood vessel progresses has a larger value.
As described above, a measurement value of the blood refill time is affected by various factors. Therefore, there arises a problem in that, when the blood refill time is measured in one body portion of the subject, it is impossible to correctly determine the condition of the cardiovascular system of the subject.
A similar problem arises in a measurement of an index related to the blood oxygen saturation. That is, also a measurement value of an index related to the blood oxygen saturation may be varied depending on the measurement location. Therefore, there is a possibility that, when the blood oxygen saturation is measured in on one body portion of the subject, it is impossible to correctly determine the condition of the cardiovascular system of the subject.
In a measurement of the blood refill time or an index related to the blood oxygen saturation which is performed only in a certain body portion of the subject, namely, there is a problem in that the condition of the cardiovascular system of the subject cannot be correctly determined.
The invention has been conducted in view of the above-discussed problem. It is a main object of the invention to provide a measuring system, measuring apparatus, and method for evaluating the condition of a patient in which the condition of the cardiovascular system of the subject can be correctly determined.